powerpc/82xx: Fix BCSR bits for MPC8272ADS boards

mpc8272_ads.c is using BCSR bits definitions from pq2ads.h, but
according to User's Guide the bits are wrong for MPC8272ADS boards
(I guess definitions from pq2ads should only be used for PQ2FADS
boards).

So, let's introduce our own definitions for MPC8272ADS, and don't
include pq2ads.h.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>